1. Field of the Invention
This invention relates to an image forming apparatus such as a copying machine, a facsimile apparatus or a printer for forming an electrostatic image on an image bearing member, for example, by an electrophotographic printing method, an electrostatic recording method or the like, and visualizing this electrostatic image as a visible image (toner image) with a developer contained in a developing apparatus, and particularly to an image forming apparatus provided with a developer supplying apparatus for supplying a developer to be supplied to a developing apparatus.
2. Related Background Art
In image forming apparatus such as a copying machine, a facsimile apparatus and a printer, there is well known a method of carrying a dry type developer as a visualizing agent on the surface of a developer carrying member, carrying and supplying the developer to the vicinity of an image bearing member bearing an electrostatic image thereon, and developing and visualizing the electrostatic image by an alternating electric field which alternately applies electrolysis to between the image bearing member and the developer carrying member, and it is usual that a developing sleeve is used as the developer carrying member and a photosensitive drum is used as the image bearing member.
As the developing method, there is known, for example, a so-called magnetic brush developing method of using a developer which is of two-component composition including toner particles and carrier particles (a so-called two-component developer), forming a magnetic brush on the surface of a developing sleeve having a magnet disposed therein, bringing this magnetic brush into frictional contact with or proximity to a photosensitive drum opposed to the developing sleeve with a minute developing gap held therebetween, and continuously applying an alternating electric field to between the developing sleeve and the photosensitive drum (between S-D) to thereby repetitively effect the shift of the toner particles from the developing sleeve side to the photosensitive drum side and the reverse shift thereof and accomplish developing.
For example, in an image forming apparatus using the two-component developer as described above, the toner is consumed with image formation and therefore, it is necessary to suitably supply the toner to a developing apparatus.
The construction of a developing apparatus for two-component magnetic brush development, and of a developer supplying apparatus for supplying a developer to the developing apparatus will hereinafter be described with reference to FIGS. 16A and 16B of the accompanying drawings. FIGS. 16A and 16B schematically show the cross sections of the developing apparatus and the developer supplying apparatus, respectively.
The developing apparatus 4 has, in a developer container (developing apparatus main body) 41, a developing sleeve 46 as a developer carrying member, a magnet roller 47 as magnetic field generating means fixedly disposed in the developing sleeve 46, a developing screw 44 and an agitating screw 45 as developer agitating means for agitating and carrying the developer in the developer container 41, a toner receiving hole 49, and a regulating blade 48 disposed to form the developer as a thin layer on the surface of the developing sleeve 46.
The interior of the developer container 41 is substantially divided into two, i.e., a developing chamber 42 and an agitating chamber 43. The developing screw 44 is disposed in the developing chamber 42, and the agitating screw 45 is disposed in the agitating chamber 43. As shown, the developing sleeve 46 is disposed in proximity to the photosensitive drum 1, and is set so as to be rotated in an opposite direction to (or the same direction as) the photosensitive drum, and be capable of effecting development with the developer D being in contact with the photosensitive drum 1.
The developer supplying apparatus 50 has a sub-toner container (first developer container 51 storing therein a developer (toner) to be supplied to the developing apparatus 4. Above the sub-toner container 51, there is formed a toner supply port 60 which can receive the supply of the toner.
Also, below the sub-toner container 51, a toner carrying pipe 52 which can carry the toner from the sub-toner container 51 is cylindrically formed while protruding in a substantially horizontal direction. In the toner carrying pipe 52, there is rotatably provided a supply screw (first supplying means) 53 having a spiral surface formed on the rotary shaft thereof. The supply screw 53 has connected thereto driving means 54 for rotatively driving this supplying screw 53.
Also, in the sub-toner container 51, there is provided a toner sensor (toner presence or absence detecting sensor) 56 for electrically or optically directly detecting the presence or absence of the toner. Further, in the sub-toner container 51, there is rotatably or pivotally movably provided an agitating member 55.
The developer supplying apparatus 50 further has a main toner container (second developer container) 57 provided above the sub-toner container 51 for storing therein the toner to be supplied to the sub-toner container 51. In the main toner container 57, there is rotatably provided an agitating and carrying member (second supplying means) 58. The agitating and carrying member 58 has connected thereto driving means 59 for rotatively driving this agitating and carrying member 58.
The main toner container 57 can also be made detachably mountable with respect to the sub-toner container 51 and an image forming apparatus main body, and is generally called a toner cartridge (or a toner bottle).
An image forming operation in the developing apparatus will now be described.
A two-component developer comprising a mixture of nonmagnetic toner particles (toner) and magnetic carrier particles (carrier) is contained in the developer container 41. The mixing ratio of the toner(T) to the carrier(C) (hereinafter referred to as the “T/C ratio”) is kept constant by an amount of toner corresponding to an amount of toner consumed by development. That is, the toner is caused to fall from the sub-toner container 51 in which the toner to be supplied is stored into the agitating chamber 43 in which the agitating screw 45 is provided via the receiving hole 49 of the developer container 41, by the supply screw 53, and is supplied to the developing apparatus 4. As methods of detecting and maintaining the T/C ratio of the developer in the developer container 41 at this time, various methods have heretofore been put into practical use.
Description will hereinafter be made of the operation of replenishing the sub-toner container 51 with the toner when the toner in the sub-toner container 51 has been decreased with the consumption of the toner.
The agitating member 55 has the action of performing rotation or pivotal movement to thereby take the toner to pieces in order to prevent the toner from lumping in the sub-toner container 51. Also, the supplying screw 53 is provided to act to carry the toner in the sub-toner container 51 in a longitudinal direction (a direction parallel to the plane of the drawing sheet of FIGS. 6A and 6B) toward the hole 49 communicating with the developer container 41 and to act to push the toner out of the hole and cause it to fall into the developer container 41. In a case where the toner sensor 56 detects the absence of the toner, whereafter the toner sensor 56 still detects the absence of the toner in spite of the operation of the agitating member 55, it is judged that the toner does not lump in a portion of the toner container 51 but has become truly absent.
Once it is judged that the toner is truly absent in the sub-toner container 51, the agitating and carrying member 58 in the main toner container 57 is rotated, whereby the toner is supplied from the main toner container 57 to the sub-toner container 51. The agitating and carrying member 58 is provided to act to be rotated to thereby take the toner to pieces in order to prevent the toner from lumping in the main toner container 57, to act to carry the toner in the main toner container 57 in a longitudinal direction (the direction parallel to the plane of the drawing sheet of FIGS. 16A and 16B) toward the toner supply port 60 communicating with the sub-toner container 51, and to act to push the toner out of the supply port 60 and cause it to fall into the sub-toner container 51, and it is usual to use, for example, a sheet material of PET or the like as this member.
The rotation of the agitating and carrying member 58 in the main toner container 57 continues until the toner sensor 56 detects the presence of the toner, and after the toner sensor 56 has detected the presence of the toner, the supply of the toner is continuedly effected from the sub-toner container 51 via the supply screw 53.
Description has been made here of a case where the agitating and carrying member 58 is rotated after the toner sensor 56 has detected the absence of the toner, but since the agitating and carrying member 58 is a sheet material, it does not push the toner into the sub-toner container 51 more than necessary and therefore, even before the toner sensor detects the absence of the toner, there is no problem even if the agitating and carrying member 58 is rotated.
Also, when the toner sensor 56 does not detect the presence of the toner even if the agitating and carrying member 58 in the main toner container 57 is rotated for a sufficient time, it can be judged that the toner is not supplied to the sub-toner container 51, that is, the toner has also become absent in the main toner container 57. The absence of the toner is informed to a user through display means such as an operation panel, not shown.
The main toner container 57 is made detachably mountable in one case, and is fixed to the apparatus in another case. In the case where it is made detachably mountable, the main toner container 57 is generally called a toner cartridge, and when the toner therein has become absent, as described above, the main toner container 57 is bodily interchanged to thereby fill it with the toner. Also, in the case where it is fixed to the apparatus, the main toner container 57 is filled with the toner directly from a discrete toner container.
The supply screw 53 is rotated by the driving means 54, and the number of revolutions or the rotation time thereof is set in conformity with the amount of toner required by the developing apparatus, and when the set number of revolutions or rotation time is reached, the rotation thereof is stopped, whereby it carries the amount of toner required by the developing apparatus, and supplies the toner to the developer container. At this time, the amount of toner to be carried per rotation or per unit time is made into a constant in advance in conformity with the sizes of the respective toner supply screws, and the control of calculating the number of revolutions or the rotation time in conformity with the required amount is possible.
Here, the amount of toner carried by the screw is proportional to the number of revolutions of the screw and therefore, to set it by the rotation time, it becomes a premise that the driving means for the screw be always rotatable at a constant speed. Also, if provision is made of means for counting the number of revolutions of the screw, it is possible to set the amount of toner to be carried by the screw by the number of revolutions even if the rotating speed of the screw is constant.
In FIGS. 16A and 16B, in order to make the figures easily seen, the longitudinal direction of the photosensitive drum 1 and the developing apparatus 41 is depicted in a direction perpendicular to the plane of the drawing sheet, and the longitudinal direction of the sub-toner container 51, the supplying screw 53 and the main toner container 57 is depicted in a direction parallel to the plane of the drawing sheet, but actually it is usual that these longitudinal directions are the same directions. Description will now be made of a driving mechanism for the developer supplying apparatus 50.
FIG. 17 of the accompanying drawings schematically shows the construction of the developing apparatus 4 and the driving mechanism 50 for the developer supplying apparatus 50.
As described above, the developing apparatus 4 can develop the electrostatic image on the photosensitive drum 1 as a visible image by the use of the developer stored therein. That is, the developing apparatus 4 has the developing screw 44 and the agitating screw 44 and the agitating screw 45 which are developer agitating means for agitating and carrying the developer in the developing apparatus 4. Also, the developer supplying apparatus 50, as described above, has the sub-toner container 51 which is the first developer container storing therein the toner to be supplied to the developing apparatus 4, the supply screw 53 which is the first supplying means for discharging the toner from the sub-toner container 51 and supplying it to the developing apparatus 4, the main toner container 57 which is the second developer container storing therein the toner to be supplied to the sub-toner container 51, and the agitating and carrying member 58 which is the second supplying means for discharging the toner from the main toner container 57 and supplying it to the sub-toner containers 51.
The driving mechanism 200 for the developer supplying apparatus 50 has a motor 80 which is rotatively driving means capable of transmitting a drive to the supplying screw 53, and a drive gear train GA as rotation transmitting means capable of transmitting the rotation of the motor 80 to the supplying screw 53. The agitating and carrying member 58 can transmit a drive from the motor 80 to the drive gear 59 through a drive gear train (not shown) provided with a clutch mechanism, as required, and can also be driven by the use of a motor discrete from the motor 80.
Further describing, the drive gear train GA has a first drive gear 81 on the motor 80 side, and a second drive gear 82 meshing with this first drive gear 81, and the second drive gear 82 is in meshing engagement with a screw driving gear 54 for driving the supply screw 53.
Control means 90 controls the rotation and stoppage of the motor 80. Also, the control means 90 controls the rotation of the developer agitating means of the developing apparatus, i.e., the developing screw 44 and the carrying screw 45, and as described above, the supply screw 53 and further, the agitating and carrying member 58.
When by the construction as described above, the supply screw 53 is to be rotated to thereby supply the toner from the sub-toner container 51 to the developing apparatus 4, the motor 80 is rotated. Thereby, it is possible to rotate the supplying screw 53 while keeping the agitating and carrying member 58 stopped. Also, it is possible to rotate the agitating and carrying member 58 while keeping the supply screw 53 stopped.
FIG. 18 of the accompanying drawings shows the layout of the driving construction of the developing apparatuses 4 (4Y, 4M, 4C, 4K) and the developer supplying apparatuses 50 (50Y, 50M, 50C, 50K) in respective image forming stations P (PY, PM, PC, PK) in an image forming apparatus 100 of a four-set tandem type. The developing apparatuses 4 and the developer supplying apparatuses 50 for a first color, a second color, a third color and a fourth color, and driving mechanisms 200 (200Y, 200M, 200C, 200K) therefor are the same as the constructions shown in FIG. 17. As shown in FIG. 18, the developing apparatuses 4 (4Y, 4M, 4C, 4K) and the developer supplying apparatuses 50 (50Y, 50M, 50C, 50K) for the four colors are provided in rows, whereby full-color printing is possible.
In the case of this system, an intermediate transfer member (intermediate transfer medium) 7 or a recording material (recording paper) is moved in the direction of arrow and images of the respective colors are superposed thereon and therefore, an image forming operation is performed with each color delayed by a time for which the intermediate transfer member 7 or the recording material is moved by a shown dimension Q.
The photosensitive drums 1 (1Y, 1M, 1C, 1K) are in contact with the recording paper or the intermediate transfer member and therefore are always rotated, but it is usual that the agitating screw 45 and the developing screw 44 as the developer agitating means in the developing apparatus 4 are rotated only for a necessary time during the image forming operation in order to minimize the deterioration of the developer. If the operation of supplying the toner from the sub-toner container to the developing apparatus is performed with the agitating screw and the developing screw in the developing apparatus 4 remaining stopped, the supplied toner stagnates near the supply port to thereby cause the clogging of the toner and the non-uniformity of the T/C ratio in the developing apparatus and therefore, it is requisite that the operation of supplying the toner from the sub-toner container to the developing apparatus be performed by all means with the agitating screw and the developing screw in the developing apparatus being rotated.
FIG. 19 of the accompanying drawings shows the time for which the agitating screw and the developing screw in the developing apparatus are rotated, and the letter T corresponds to the time for which the recording paper or the intermediate transfer member is moved by the dimension Q in FIG. 18. Thus, as shown in FIG. 19, during the time when the agitating screw and the developing screw in the developing apparatus for each color are rotated, the supply screw as the toner supplying means of the corresponding developer supplying apparatus is rotated to thereby perform the operation of supplying the toner from the sub-toner container to the developing apparatus.
The conventional image forming apparatus has required a number of motors providing the rotative driving sources of the supply screws for supplying the toner from the sub-toner container to the developing apparatus at optimum timing for each color which correspond to the number of the supply screws.
Therefore, assuming that multiplex development of four colors is to be effected, four motors have been necessary only for driving the supplying means. For example, it is possible to make some motors common to one another and utilize an electromagnetic clutch to change over rotation and stoppage, but of course, after all, an electromagnetic clutch becomes necessary in place of the motors.
For example, Japanese Registered Utility Model No. 3060562 discloses a developer supplying mechanism of a construction in which by a single driving motor, a driving side is selected and changed over depending on the rotation direction of the motor, to thereby drive the respective developer supplying rollers of two toner containers. Also, as the drive changeover method, use is made of a rockable gear, a one-way clutch or the like. By this construction, it is possible to decrease the number of motors.
Japanese Registered Utility Model No. 3060562, however, bears no description about the relation between the rotated state of the agitating screw and the developing screw in the developing apparatus and the operated state of the supply screw of the developer supplying apparatus, i.e., the drive changeover timing.
According to the results of our numerous studies and experiments, it has been found that to suppress the scattering of the developer, background fog and density fluctuation due to the faulty agitation of the developer, and obtain a good image, it is very important to optimize the drive changeover timing in conformity with various kinds of information.